Various forms of contact units are used in contact probes for open/short tests, environmental tests and burn-in tests of semiconductor devices and printed circuit boards. The contact units are also used in sockets for semiconductor devices which may be in the forms of bare chips, LGA (and grid array), BGA (ball grid array), CSP (chip side package) and so forth. Electric connectors may also use such contact units.
Recently with the increase in the frequency of the signals that are required to be processed by semiconductor devices, it has become necessary for the contact units for the sockets of semiconductor devices and the contact probes for testing semiconductor devices to be able to handle high frequency signals of up to several hundred MHz. In particular, the contact units are required to have a lower electric inductance and resistance more than before.
Also, such electroconductive contact units are required to be compact in size so as to be arranged extremely close to each other, and to be provided with a sufficient resiliency so as to accommodate any irregularities in the surface states of the parts to be contacted. Japanese patent publication No. 8-15171 discloses the use of a coil member consisting of a compression coil spring having contact pin sections defined, at either axial end, by straight terminal sections of the coil wire of the compression coil spring. It also teaches that the terminal ends of the compression coil spring may be made relatively firm by reducing the coil diameter and/or reducing the coil pitch. However, because this conventional contact unit uses the compression coil spring as an internal conductor, the electric signal is conducted along a spiral path, and therefore encounters a substantial electric inductance. The electric resistance of the compression coil spring may also create a problem.